Diamond-coated hard material, throwaway insert and a process for the production thereof

Abstract

PCT No. PCT/JP91/01359 Sec. 371 Date Jul. 14, 1992 Sec. 102(e) Date Jul. 14, 1992 PCT Filed Oct. 4, 1991 PCT Pub. No. WO92/05904 PCT Pub. Date Apr. 16, 1992.An object of the present invention is to provide a diamond-coated hard material having a high bonding strength to a substrate and a diamond-coated throwaway insert capable of cutting various light alloys such as Al-Si alloys at a high cutting rate for a long time. This object can effectively be attained by a diamond-coated hard material comprising a sintered body consisting of Si3N4 as a predominant component, at least a part of the sintered body having a sintered surface at least a part of which is coated with diamond and a diamond-coated throwaway insert having a diamond- or diamond-like carbon-coated layer with a thickness of 0.1 to 200 mu m, deposited from gaseous phase, on the surface of a substrate consisting of Si3N4, as a predominant component, in which the surface state of the substrate is maintained as sintered and a part or whole of the sintered surface is coated with the diamond- or diamond-like carbon-coated layer.

We claim: 
     
       1. A diamond-coated hard material comprising a sintered body consisting of Si 3  N 4  as a predominant component, at least a part of the sintered body having a sintered surface at least a part of which is coated with diamond. 
     
     
       2. A diamond-coated hard material having a diamond-coated layer formed on the surface of a hard material consisting of Si 3  N 4  as a predominant component, in which: (1) microscopic roughness is present on the surface of the substrate,   (2) at least one protrusive part is present in the standard length of 10 μm in a diamond-coated layer and substrate interface,   (3) the ratio of sum A of the lengths of dent parts to sum B of the lengths of the protrusive parts is in the range of 0.05≦A/B≦20 in the standard length in the interface, and   (4) the protrusive parts are intruded into the diamond-coated layer.   
     
     
       3. A diamond-coated hard material having a diamond- and/or diamond-like carbon-coated layer formed on the surface of a hard material consisting of Si 3  N 4  as a predominant component, in which: (1) microscopic roughness is present on the surface of the substrate and   (2) the protrusive parts are defined by a surface roughness represented by an Rmax of 1.5 to 30 μm in the standard length of 50 μm in the diamond-coated layer and substrate interface.   
     
     
       4. The diamond- or diamond-like carbon-coated hard material as claimed in claim 2 or 3, wherein the protrusive parts are intruded into the diamond-coated layer by at least 0.2 μm. 
     
     
       5. The diamond- or diamond-like carbon-coated hard material as claimed in any of claims 2 to 4, wherein the protrusive parts are composed of silicon nitride crystals and/or silicon nitride-containing crystals and/or sialon. 
     
     
       6. A diamond-coated throwaway insert having a diamond- or diamond-like carbon-coated layer with a thickness of 0.1 to 200 μm, deposited from gaseous phase, on the surface of a substrate consisting of Si 3  N 4  as a predominant component, in which the surface state of the substrate is maintained as sintered and a part or whole of the sintered surface is coated with the diamond- or diamond-like carbon-coated layer. 
     
     
       7. The diamond-coated throwaway insert as claimed in claim 6, in which at least a part or whole of each of the rake face and flank face of the insert is coated with the diamond- or diamond-like carbon-coated layer in such a manner that only the upper and lower surfaces of the sintered throwaway insert substrate or the rake face is ground and the flank face is maintained as sintered. 
     
     
       8. The diamond-coated throwaway insert as claimed in claim 6, in which a part or whole of each of the edge-treated surface, the rake face and flank face of the insert is coated with the diamond- or diamond-like carbon-coated layer in such a manner that the sintered throwaway insert substrate is subjected to an edge treatment, only the upper and lower surfaces or the rake face is ground and the flank face is maintained as sintered. 
     
     
       9. The diamond-coated throwaway insert as claimed in claim 6, in which a part or whole of each of the edge-treated surface, the rake face and flank face of the insert is coated with the diamond- or diamond-like carbon-coated layer in such a manner that the sintered throwaway insert substrate is subjected to an edge treatment, the upper and lower surfaces or the rake face and the flank face are maintained as sintered. 
     
     
       10. The diamond-coated throwaway insert as claimed in claim 6, in which a part or whole of the sintered throwaway insert substrate is ground and optionally subjected to an edge treatment, and is then subjected to a heat treatment to maintain the whole surface of the insert as heat-treated, and a part or whole of each of the edge-treated surface, the rake face and flank face of the insert is coated with the diamond- or diamond-like carbon-coated layer. 
     
     
       11. The diamond-coated throwaway insert as claimed in claim 6, in which a part or whole of the sintered throwaway insert substrate is ground and optionally subjected to an edge treatment, and is again subjected to a heat treatment to maintain the whole surface of the insert as heat-treated, and after grinding a partial or whole surface of the insert, a part or whole of each of the edge-treated surface, the rake face and flank face of the insert is coated with the diamond- or diamond-like carbon-coated layer. 
     
     
       12. The diamond-coated hard material or diamond-coated throwaway insert as claimed in anyone of claims 1 to 11, wherein a freely grown columnar or hexagonal pillar crystal structure of Si 3  N 4  is present on the surface of the insert substrate. 
     
     
       13. The diamond-coated hard material or diamond-coated throwaway insert as claimed in claim 12, wherein the Si 3  N 4  columnar or hexagonal pillar crystal has a mean major axis/minor axis ratio of 1.5. 
     
     
       14. The diamond-coated hard material or diamond-coated throwaway insert as claimed in claim 12, wherein at least a part of the Si 3  N 4  columnar or hexagonal pillar crystal has a mean major axis of at least 2 μm. 
     
     
       15. A process for the production of a diamond-coated throwaway insert, which comprises sintering a mixed powder to be a substrate, comprising Si 3  N 4  powder containing at least 50 % of a Si 3  N 4  , as a predominant component, and 1 to 50 wt % of at least one sintering assistant selected from the group consisting of Al 2  O 3 , Y 2  O 3  MgO AlN and SiO 2  at a temperature of 1,600° to 2,000° C. in a gaseous N 2  atmosphere for 30 minutes to 5 hours, converting at least the rake face thereof into a sintered surface or heat-treated surface and then coating at least the rake face with diamond. 
     
     
       16. The process for the production of a diamond-coated throwaway insert, as claimed in claim 15, wherein the heat-treated surface is obtained by grinding the silicon nitride sintered body and then subjecting to a heat treatment at a temperature of 1,300° to 2,000° C. in N 2  gas or an inert gas atmosphere of 1 to 3,000 atm.